I went to Autozone - they rent tools like the chain cutter and pipe expander. They run you credit card for the cost of the tool and when you return it they credit it all back to your card. Hard to beat Free.
I needed the pipe expander to get my X pipe on.

I second the "chain type" pipe cutter. I just did a Corsa X-Pipe and Corsa Indy Pace Car mufflers. Without this tool it would have been much more difficult. If you have an "Oreilly Auto Parts or similar store, check their "tool loaner" program. I borrowed the tool...brand new never used for a small deposit! Worked great!

I will be doing my Corsa Xpipe soon. What size chain cutter should I look for ? 14" handle 16" 18 " ??

I went to Autozone - they rent tools like the chain cutter and pipe expander. They run you credit card for the cost of the tool and when you return it they credit it all back to your card. Hard to beat Free.
I needed the pipe expander to get my X pipe on.

chain is easier to re weld. when i was just out of HS and working in a shop all we did was sawzall exhausts. exhaust pipe has a lot of carbon and junk in the steel from the engine running. when you go to reweld with carbon steel and 75/25 gas it spatters and is just that much harder to keep a clean bead going. the smoother the cut the easier it is to reweld. also, if the exhaust is stainless use 308 wire and helium trimix if you can. the 75/25 will introduce some carbon into the weld. it usually won't rust too much if you use 308 wire but it will more than using helium

shops use the sawsall because they are fast. the chain cutter will take 5x a long to use but it's much cleaner

I figure an exhaust pipe cutter won't work since I won't be able to get all the way around the pipe at the top where it's closest to the car's floor (right?).
Torch is no good since I would likely hurt myself or the car.
So a reciprocating saw is my only option... right?

Reciprocating saw would be my choice

Whatever you do, put a piece of metal at the top so you do NOT punch a hole in the floor board - regardless of where you cut!

I went to Autozone - they rent tools like the chain cutter and pipe expander. They run you credit card for the cost of the tool and when you return it they credit it all back to your card. Hard to beat Free.
I needed the pipe expander to get my X pipe on.

This is the best answer! Second would be to google exhaust pipe cutter.

For most respondents, I would never let them touch any of my cars. Geeze!